JUVENILE-HORMONE ESTERASES IN DIAPAUSE AND NON-DIAPAUSE LARVAE OF THE EUROPEAN CORN-BORER, OSTRINIA-NUBILALIS

Hemolymph levels of juvenile hormone esterase, 1-naphthyl acetate esterase and juvenile hormone were measured in synchronously staged diapause and nondiapause larvae of the European corn borer, O. nubilalis. Juvenile hormone esterase levels were monitored using juvenile hormone I as a substrate while juvenile hormone titers were measured with the Galleria bioassay. Hemolymph of nondiapause larvae showed 2 peaks of juvenile hormone hydrolytic activity: 1 near the end of the feeding phase and a smaller 1 just prior to pupal ecdysis. These peaks of enzyme activity correlated with the low levels of hemolymph juvenile hormone. Juvenile hormone titers were high early in the stadium then showed a 2nd peak during the prepupal stage coinciding with low esterase activity. Diapause hemolymph had peak juvenile hormone esterase activity nearly 4 times the nondiapause level, reaching a peak near the end of the feeding phase. Diapause-destined larvae retained high juvenile hormone titers even during the rise of the high esterase levels. 1-Naphthyl acetate esterase levels did not correlate with the juvenile hormone esterase levels in either the diapause or nondiapause hemolymph. High levels of 1-naphthyl acetate esterase activity were associated with molting periods.